Process for the production of free-cutting carbon steels with special deoxidation

ABSTRACT

Process for the production of free-cutting carbon steels, wherein during the deoxidation CaSiAl and CaMnSiAl ferro-alloys are combinedly used as deoxidants in such a way that the proportion of the two deoxidants in the used deoxidating addition depends on the C-content of the steel. The two deoxidants are added according to the following relation: X1 . (C % - 0.15) . 8(kg/t) CaSiAl + + X2 . (0.65 - C %) . 8 (kg/t) CaMnSiAl WHERE THE VALUE OF X1 AND X2 IS 70/Si % + OR - 10% and Si % means the Si-content of the respective desoxidant.

United States Patent Csepanyi et al.

PROCESS FOR THE PRODUCTION OF FREE-CUTTING CARBON STEELS WITH SPECIAL DEOXIDATION Inventors: Sandor Csepanyi; Sandor Enekes,

both of Miskolc; Guido Temesszentandrasi, Budapest; Pal Zambo, Miskolc; Zoltan Palmay, Ozd, all of Hungary Assignees: Lenin Kohaszati Muvek,

Miskolc-Diosgyorvasgyar; Ozdi Kohszati Uzemek, Ozd, Hungary Filed: May 26, 1971 Appl. No.: 147,223

Foreign Application Priority Data May 29, 1970 Hungary 01-128 US. Cl. 75/58, 75/129 Int. Cl C2lc 7/00 Field of Search 75/58, 129

[56] References Cited UNITED STATES PATENTS 3,301,663 1/1967 Wicher et a1. 75/58 3,304,174 2/1967 Ototani et al..... 75/58 X 3,383,202 5/1968 Lynch ....75/58 X 3,575,695 4/1971 Miyashita et a1. 75/58 X Primary ExaminerL. Dewayne Rutledge Attorney-Young & Thompson [57] ABSTRACT Process for the production of free-cutting carbon steels, wherein during the deoxidation CaSiAl and CaMnSiAl ferro-alloys are combinedly used as deoxidants in such a way that the proportion of the two deoxidants in the used deoxidating addition depends on the C-content of the steel. The two deoxidants are added according to the following relation:

x (C 0.15) 8(kg/t) CaSiAl +x (0.65 C 8 (kg/t) CaMnSiA] where the value of x and x is 70/Si i 10% and Si means the Si-content of the respective desoxidant.

4 Claims, No Drawings PROCESS FOR THE PRODUCTION OF FREE-CUTTING CARBON STEELS WITH SPECIAL DEOXIDATION The object of the invention is a process for the production of free-cutting carbon steels, applying a special deoxidation in order to improve the cutting properties.

In modern industrial production the temporal harmonization of the production process is of great importance. Therefore, in the machining shop the importance of not only good but also uniform machinability of the processed material is constantly increasing, in order to maintain the technological characteristics within the permissible limits. For a long time, only the so-called automatic steels have met this requirement. In the last decade, however, efforts were made for extending this requirement to other steel qualities.

According to the recent investigations published in the technical literature, during the machining of carbon steels a non-metallic deposit occurs on the surface of the carbide cutting tools containing TiC from the deoxidation products always present in the machined steel which considerably increases the tool life. This nonmetallic deposit is not identical with the so-called builtup edge occurring with low cutting speeds, which consists of metallic phases and is well known in the cutting technology.

It was proved that in order to provide for the above mentioned non-metallic deposit protecting the tool, the carbon steel to be machined must be deoxidated by adding a complex ie a multicomponent alloying element, the composition of which is: 75 to 90 Si, 4 to Ca and maximum 2 A]. It was determined by investigations that when using the deoxidant of said composition the carbon steel is free-cutting with respect to the tool-life, if its oxygen content amounts to at least 0.005 and the proportion of A1 0 in the oxide inclusions is not more than 35 The thickness of the non-metallic wear-preventive deposit occurring on the carbide cutting tool containing TiC varies as a function of the temperature and pressure occurring on the tool surface. If a given steel quality is machined so that from the technological characteristics only the cutting speed is increased, then under the effect of the temperature increasing together with the cutting speed the viscosity of the above mentioned non-metallic layer decreases, whereby the layer is squeezed out from under the chips. Thereby a certain range of the cutting speed is determined within which the best tool life can be achieved. If the strength of the machined steel is higher, the pressure on the tool will be higher, too, thus the upperand lower limits of the advantageous cutting speed range are shifted towards the lower speeds. Here, the shifting of the upper speed limit is of greater extent, therefore the optimum cutting speed range is even reduced during the shifting.

The invention aims at the development of a deoxidation technology of carbon steels whichprovides for a machinability better than that of the above mentioned steels.

The machinability of carbon steels produced with the use of the process according to the invention is better than that of the steels known up to now because the proportion of deoxidants varies as a function of the C- content. Thus, when cutting carbon steels of maximum 0.65 C-content, a highly effective wear-impeding nometallic deposit occurs on the tool within a wide cutting speed range which multiplies the tool life. The narrowing down of the optimum cutting speed range observable with carbon steels made with the process known up to now, does not occur with the machining of carbon steels produced with the process according to the invention.

The basic idea of the invention is the recognition that in case of various carbon steels the machinability determined by the edge life of the carbide tool is uniform and can be maintained at a suitable level within a wide range of the cutting speeds, if CaSiAl and CaMnSiAl ferro-alloys are combinedly added as deoxidants during the deoxidation in such a way that the proportion of the two deoxidants in the used deoxidating addition depends on the C-content of the steel.

According to the invention, in the CaSiAl ferro-alloy the ratio of the weight percent of Ca Si must be between 1 5 and l 10, whereas the ratio of the weight percent of Al Si must be lower than 1 35.

According to the invention, in the CaMnSiAl ferroalloy, the ratio of the weight percent of Ca Si must be between 1 20 and l 10, whereas the Mn-content must be between 10 to 20 by weight and the Alcontent maximum 1.5 by weight.

The above two desoxidants must be added, depending on the C-content of the steel, according to the following formula, in the case of carbon steels having a C- content of maximum 0.65 of weight, and a Si-content of usually 0.17 to 0.65 of weight:

x (C 0.15). 8 (kg/t)CaSiAl+ x (0.65 C 8 (kg/t) CaMnSiAl In the above formula, the value of the multiplicators .t and x is /Si i 10 where Si always means the Si-content of the ferro-alloy CaSiAl and CaMnSiAl, respectively, in weight per cent.

As a result of adding the CaSiAl and CaMnSiAl deoxidants, respectively, in the ratio according to the invention inclusions occur which become plastic at different temperatures and pressures. The combined adding of the two deoxidants in the above given ratio ensures that the hot strength of deoxidizing products remaining in the steel will be nearly proportional to the strength of the carbon steel. Thus, with the carbon'steels used in practice the tool-protecting non-metallic deposit is formed during machining in a wide range of the cutting speed. At the same time, it can be ensured that the above mentioned narrowing-down of the cutting-speed,

dangerous from a technological point of view, will not occur with the increase of the C-content.

In order to ensure the uniform distribution of deoxidants and deoxidation products of' composition and ratio determined according to the invention, it is expedient to add the medium-size annealed alloy elements, half into the tap ladle before tapping, and half into the steel stream during tapping at one third fullness of the ladle. At first always the CaMnSiAl alloy should be added. If e.g. the weight of this material is more than the half of the total weight of the deoxidants depending on the C-content of the steel, then the CaMnSiAl of weight corresponding to half of the total weight is added into the ladle, and the remainder is placed in the feed chute in order to add into the steel stream with the CaSiAl alloy.

The practical application of the process according to the invention is illustrated by way of two numerical examples.

EXAMPLE 1 Deoxidation of a free-cutting 0.25 C carbon steel is carried out in an open-hearth (Siemens-Martin) furnace. The tapping is carried out into a ladle.

Composition of ferro-alloys applied for the deoxidation:

CaSiAl: Ca 10 by weight, Si 70 by weight, A1 1.5

% by weight, Fe the remainder.

CaMnSiAl:Ca 5 by weight, Mn 16 by weight, Si

60 by weight, A1 0.8 by weight, Fe the remainder.

The two alloys correspond to the specification according to the invention, since the proportion of their constituents falls between the limits given by the invention:

In case of CaSiAl:

Ca:Si :70 1:7

Al:Si 1.5:75 1:50 In case of CaMnSiAl:

Ca:Si 5:60 1:12

The multiplicators x and x in the formula according to the invention, serving for the determination of the proportion of the above mentioned two ferro-alloys is, calculated on the basis of the example:

The specific quantity of the desoxidating alloys to be fed is, calculated by the mean C-content of 0.25 of the steel:

CaSiAl 1.00 (0.25 0.15) 8 (kg/t) 0.8 kg/t CaMnSiAl= 1.17 (0.65 0.25) 8 (kg/t)= 3.7 kg/t The quantity of the deoxidating alloys to be fed, related to the total batch, i.e. to 100 tons, is

CaSiAl 80 kg CaMnSiAl 370 kg Total 450 kg The annealing of the deoxidating alloys to be fed is finished in the last 8 hours before the production and the alloys are crushed so that the proportion of pieces smaller than 10 mm does not exceed 10 and should not contain pieces larger than 120 mm.

Before tapping 450 2 225 kg of CaMnSiAl is added in the ladle, 370 225 145 kg thereof is prepared in the charger. Over the latter, 80 kg of CaSiAl is placed. The material from the feed chute is fed during the tapping at one third fullness of the ladle.

EXAMPLE 2 Deoxidation of 0.45% C carbon steel is conducted as in Example 1, using the ferro-alloy of the same composition as in Example 1, whereby the multiplicators of the formula determining the feeding ratio are:

x, 1.00 and x 1.17, just as in Example 1.

The specific quantity of the deoxidating alloys, calculated from the mean C-content of 0.45 of the steel, according to the invention, is as follows:

CaSiAl 1.00 (0.45 0.15) 8 (kg/t) 2.4 (kg/t) CaMnSiAl 1.17 (0.65 0.45) 8 (kg/t) 1.9

The quantity of the deoxidating alloys, related to the total charge, i.e. to tons is CaSiAl 240 kg CaMnSiAl 190 kg Total 430 kg With the annealing and crushing of the deoxidating alloys the same procedure is followed, as in Example 1.

Before tapping, half of the total quantity of the deoxidants, i.e. 430 2 215 kg is added in the ladle. Thereof 190 kg is CaMnSiAl, the remaining 25 kg is CaSiAl. The other 215 kg of CaSiAl is placed in the charger, wherefrom it will be fed during the tapping at one third fullness of the ladle.

By means of the process according to the invention carbon steels of maximum 0.65 C-content can be produced in a controllable manner the machinability of which is considerably better related to the carbon steels known at present, calculated on the basis of the tool life in a broad range of the cutting speed, and whose tool life is multiplied.

What we claim is:

1. Process for the production of free-cutting carbon steels, comprising providing CaSiAl and CaMnSiAl ferro-alloys as deoxidants, where the weight per cent ratio of Ca:Si in the CaSiAl ferro-alloy is between 1:5 to 1:10, the weight per cent of Al:Si amounts to maximum 1:35, whereas in the CaMnSiAl ferro-alloy the Ca:Si ratio amounts to 1:20 to 1:10, the Mn-content is 10 to 20% by weight, the Al-content maximum 1.5% by weight, and adding the two deoxidants to molten carbon steel according to the following relation depending on the C-content of the steel to be produced:

x, (C 0.15) 8 (kg/t) CaSiAl +x (0.65 C 8 (kg/t) CaMnSiAl where the value of x, and x is 70/Si i 10% and Si means the Si-content of the respective deoxidant.

2. Process according to claim 1, wherein the deoxidizing alloys to be fed to the molten steel are finished annealed in the last eight hours and crushed before being added so that the proportion of pieces smaller than 10 mm is maximum 10%, the size of the largest pieces being not more than mm.

3. Process according to claim 1, wherein half of the total quantity of the two deoxidants is added in a ladle before tapping, whereas the other half is added into the steel stream during the tapping at one third fullness of the ladle.

4. Process according to claim 3, wherein the CaMn- SiAl alloy is added first. 

2. Process according to claim 1, wherein the deoxidizing alloys to be fed to the molten steel are finished annealed in the last eight hours and crushed before being added so that the proportion of pieces smaller than 10 mm is maximum 10%, the size of the largest pieces being not more than 120 mm.
 3. Process according to claim 1, wherein half of the total quantity of the two deoxidants is added in a ladle before tapping, whereas the other half is added into the steel stream during the tapping at one third fullness of the ladle.
 4. Process according to claim 3, wherein the CaMnSiAl alloy is added first. 